We previously observed an association between a 92 kDa gelatin type IV collagen degrading metalloproteinase and malignancy. This enzyme, together with a 67 kDa gelatinase/type IV collagenase, was found to be incapable of degrading native type IV collagen in solution and in tissue sections. However, both enzymes readily degraded denatured and pepsin cleaved type IV collagen. The organic mercurial compound, APMA, reported to activate collagenases, reduced the molecular weight of both gelatinases under study, but did not enhance their collagenolytic activity. Plasmin was found to directly degrade both native and denatured type IV collagen. Similarly, exogenous plasminogen mediated type IV collagen degradation, when added to culture supernatants from cell lines expressing plasminogen activators. This collagen degradation was independent of metalloproteinase activity. To study the relative importance of metalloproteinases in tumor invasion and metastases, we have isolated cDNA clones for four members of this proteinase family. These include 1.8 kbp mammalian collagenase clone, 1.6 kbp 67 kDa gelatinase clone, 0.9 kbp 92 kDa gelatinase clone and 0.37 kbp stromelysin clone. DNA sequencing has revealed virtually 100% homology to the published sequence of all four clones. They are presently being used to assess metalloproteinase expression in a variety of normal and neoplastic cell lines and tissue sections.